For Mac, I haven't written anything. In principle, you can do it manually by dumping the iTunesLocalized.qtr file using a tool called DeRez. I believe this tool is part of the XCode installation. Open the dumped text file and find the "List Contents (Small)" resource. That'll give you the hex for that font resource record.

Then, with a hex editor, open iTunesLocalized.qtr and search for the hex you got from the dumped text file.

The second byte of the hex is the font size. E.g. if the hex is "0008", the font size is 8pt. Change the second byte there to the font size you want.